Magnetic induction devices (MIDs), such as transformers, inductors, loop antennas, Baluns (Balun—Balanced-Unbalanced), etc., are used in many applications, such as communication network applications, power circuit applications, test equipment, and radio-frequency (RF) applications.
In addition to traditional techniques of wire winding, there is a continuous search for new technologies that may eliminate the need for actual winding of wires. Some new techniques use integrated circuit (IC) fabrication technologies or printed circuit board (PCB) fabrication technologies for producing planar structures or multilayer structures that are intended to replace wire windings.
MIDs produced by IC fabrication technologies typically include multiple stacked layers. The layers are typically thin and the resultant MIDs are usually too small for many applications. Additionally, MIDs produced by IC fabrication technologies typically have air cores which limit applicability of such MIDs for various applications, such as for low-frequency communication applications and power applications.
Some IC fabrication technologies are focused on constructing thick stacked layers. One advantage of using such thick layers is the ability to produce MIDs with magnetic cores rather than with air cores. However, the overall size of MIDs produced using such thick layers is still small for many applications.
Planar transformers are typically produced using PCB or IC fabrication technologies. In such fabrication technologies, a planar spiral of conductive material is produced in one or more layers of a set of stacked layers, and in some cases, a spiral of one layer is connected to a spiral of a neighbor layer to provide a winding.
Some aspects of technologies and material that may be useful in understanding the present invention are described in the following publications:    an article entitled “Novel and high-yield fabrication of electroplated 3D micro-coils for MEMS and microelectronics”, by Yoon et al, SPIE Conference on Micromachining and Microfabrication Process Technology IV, Santa Clara, Calif., September 1998, SPIE Vol. 3511, pages 233-240;    an article entitled “Fabrication of three-dimensional inductor coil using excimer laser micromachining”, by Jolic et al, in Journal of Micromechanics and Microengineering, 13 (2003), pages 782-789;    an article entitled “Fabrication and Characterization of a Solenoid-Type Microtransformer”, by Rassel et al, in IEEE Transactions on Magnetics, Vol. 39, No. 1, January 2003, pages 553-558;    an article entitled “Photolithographic structuring of a thin metal film coil on a Zerodur cylinder”, by Siewert et al, Surface & Coating Technology 200 (2005) 1061-1064;    an article entitled “Laser-Lathe Lithography—a Novel Method for manufacturing Nuclear magnetics Resonance Microcoils”, by Vincet Malba et al, Biomedical Microdevices 5:1, 21-27, 2003;    an article entitled “Powering efficiency of inductive links with inlaid electroplated microcoils”, by Jie Wu et al, in Journal of Micromechanics and Microengineering, 14 (2004) 576-586;    Published PCT application 2006/064499 of Axelrod et al; and
the following U.S. patents:    U.S. Pat. No. 1,994,767 to Heintz;    U.S. Pat. No. 3,123,787 to Shifrin;    U.S. Pat. No. 3,874,075 to Lohse;    U.S. Pat. No. 5,793,272 to Burghartz et al;    U.S. Pat. No. 5,834,825 to Imai;    U.S. Pat. No. 6,008,102 to Alford et al;    U.S. Pat. No. 6,351,204 to Yamasawa et al;    U.S. Pat. No. 6,417,754 to Bernhardt et al;    U.S. Pat. Nos. 6,445,271 and 6,498,557 to Johnson;    U.S. Pat. No. 6,642,827 to McWilliams et al;    U.S. Pat. No. 6,831,544 to Patel et al; and    U.S. Pat. No. 6,852,605 to Ng et al.